1. Field of the Invention
The present invention relates to a mortise lock and, more particularly, to a mortise lock having a double locking function that a latchbolt is also locked together with locking of a deadbolt.
2. Description of the Related Art
Generally, a mortise lock, which is installed on various kinds of doors, includes a deadbolt and a latchbolt. The deadbolt has a locking function, and the latchbolt is moved by a door handle to go in and out the door. A conventional mortise lock is disclosed in U.S. Pat. No. 6,393,878, WO 01/42600, and so on.
The deadbolt of the conventional mortise lock performs a manual locking function by a user or an automatic locking function. On the other hand, the latchbolt simply goes in and out. Therefore, the mortise lock causes security problems since an invader can readily open a door by forcedly breaking the deadbolt only, while the mortise lock is required to provide security.
In addition, the conventional mortise lock may not perform an effective locking function due to sagging or distortion of the door after several months of installation. Moreover, the deadbolt and the latchbolt typically have a small step therebetween. Therefore, when a user pulls the door to determine whether the door is locked or not after rotating the door, the door is pulled by a length of the step to cause the deadbolt to be damaged so that the door may be malfunctioned or broken.